Method of manufacturing an optical reflector

ABSTRACT

The invention proposes a method of manufacturing a hollow optical reflector of the type which comprises a rear body overmolded around the convex rear external face of a front insert, the concave front internal face of which is covered with a reflective layer, the method comprising:  
     a step of producing the insert by forming;  
     a step of overmolding the body on the insert; and  
     a step of depositing the reflective layer on the concave front face of the insert;  
     wherein the step of depositing the reflective layer is prior to the forming step.

FIELD OF THE INVENTION

[0001] The invention proposes a method for the manufacture of an opticalreflector.

BACKGROUND OF THE INVENTION

[0002] The invention proposes more particularly a method ofmanufacturing a hollow optical reflector of the type which comprises arear body overmoulded around the convex rear external face of a frontinsert, the concave front internal face of which is covered (inparticular at least partially) with a reflective coating, the methodcomprising:

[0003] a step of producing the insert by forming;

[0004] a step of overmoulding the body on the insert; and

[0005] a step of depositing the reflective layer on the concave frontface of the insert (or on at least part of said face).

[0006] Such optical reflectors are generally used in the motor industryfor manufacturing lights or headlights for equipping motor vehicles.

[0007] The reflective face of an optical reflector is generally concaveand its generator is designed so as to obtain a light beam of givenconformation.

[0008] Production of optical reflectors by moulding of a thermoplasticmaterial, and then coating of the functional internal concave face witha reflective layer which is for example aluminium-based, are known.

[0009] However, when the surface of the mould is degraded, or else whenit is not at an optimum temperature, the surface of the componentobtained has irregularities and rough patches which, even after coatingwith the reflective layer, are detrimental to the quality of the lightbeam.

[0010] In order to remedy this problem, a proposal has been made to usea surfacer which fills in the various rough patches of the surface ofthe moulded component in order to form a smooth surface and which isnext coated with the reflective layer.

[0011] However, when the reflective face has a complex shape, and it hassharp edges, the surfacer generally has a tendency to make these edgessmoother, so that it also is detrimental to the quality of the lightbeam.

[0012] The document EP-A-0 727 677 proposes to produce the reflectiveface on an insert produced from a sheet of thermoformed plasticmaterial, to overmould the body of the optical reflector on faces of theinsert which are not intended to form the light beam, and then to coatthe functional concave surface with the reflective layer.

[0013] The thermoforming of the plastic sheet makes it possible to havereflecting surfaces of very high quality and which are not impairedduring moulding of the body. However, in the case of a complexreflecting surface, certain areas are sometimes difficult to access, sothat the whole reflecting surface is not sufficiently fully covered bythe reflective layer.

SUMMARY OF THE INVENTION

[0014] In order to remedy these drawbacks, the invention proposes amethod of the type described previously, characterised in that the stepof depositing the reflective layer is prior to the forming step.

[0015] According to other characteristics of the invention:

[0016] the step of forming the insert is a step of thermoforming asheet;

[0017] the moulding step consists of injecting into a mould a mixturewhich is composed of the material constituting the body and a gas inliquid form and which is capable of forming a foam in the mould;

[0018] during the moulding step, the front face of the insert rests on aprotuberance of a block of the mould which has a shape complementary tothat of the front face.

[0019] Other characteristics and advantages of the invention will emergefrom a reading of the following detailed description, for theunderstanding of which reference should be made to the accompanyingfigures, amongst which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIGS. 1 to 3 are schematic views in perspective which depict thesuccessive stages of the step of thermoforming the insert from athermoplastic sheet, in accordance with the invention;

[0021]FIGS. 4 and 5 are longitudinal and transverse sections of theinsert and the mould depicting the successive stages of the step ofovermoulding the body in accordance with the invention;

[0022]FIG. 6 is a longitudinal section on a larger scale of the opticalreflector obtained by the method in accordance with the invention; and

[0023]FIG. 7 is a perspective view from below of the optical reflectorobtained after the overmoulding step depicted in FIGS. 4 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] For the description of the invention, the vertical, longitudinaland transverse orientations in accordance with the indicators V1, L1, T1and V2, L2 and T2 shown in the figures will be adopted non-limitatively.

[0025] The direction from back to front as being the longitudinaldirection and from right to left referring to FIG. 4 will also beadopted.

[0026] In the description which follows, identical, similar or analogouselements will be designated by the same reference numbers.

[0027]FIG. 7 depicts an optical reflector 10 which is a hollow elementproduced in two parts. It has a concave insert 12 which is produced froma sheet of thermoformed plastic material 14, and which has a concavefront internal face 18 which is covered with a reflective layer 20 inparticular an aluminium-based one, and a convex rear external face 22.

[0028] The optical reflector 10 also has a body 16, which gives thereflector 10 its structural rigidity, and which is overmoulded aroundthe rear face 22 of the insert 12.

[0029] FIGS. 1 to 5 depict the successive steps of a method of producingthe optical reflector 10, in accordance with the invention.

[0030] According to a first step of the method, not depicted, a firstfront face 14 a of the sheet 14 is coated with a reflective layer 20based on aluminium or another reflective material, by any known method,for example by vacuum deposition or by another method such as PhysicalVapour Deposition (PVD) or Plasma Enhanced Chemical Vapour Deposition(PECVD).

[0031] A second step of the method depicted in FIGS. 1 to 3 consists ofproducing the insert 12 by forming the sheet 14.

[0032] For this, a die 24 is used, the shape of which is determined sothat the first face 14 a of the sheet 14 takes the shape of the die 24in order to form the first faces 18 of the insert 12.

[0033] Here, the die 24 is in relief, and the sheet 14 is thereforepositioned with its first face 14 a facing the die 24 so that the frontface 18 is concave.

[0034] Conversely, and according to a variant, not depicted, the die 24is hollow and the sheet 14 is then positioned with its first face 14 aopposite to the die 24.

[0035] The sheet 14 is made from a thermoplastic material, for examplepolycarbonate. Thus, for forming of the sheet 14, the latter is heatedand then applied onto the die 24. So that the sheet 14 takes the exactshape of the die 24, a vacuum is produced between the sheet 14 and thedie 24, so as to flatten the sheet against the die 24.

[0036] In a variant, without departing from the scope of the invention,the thermoforming can be achieved by other technologies well known inthe art.

[0037] The insert 12 is then obtained which, as depicted in FIG. 3, isremoved from the mould after cooling, and its edges 26 are cut.

[0038] According to a third step of the method, depicted in FIGS. 4 and5, the insert 12 is placed inside a mould 28 for overmoulding of thebody 16 around the rear face 22 of the insert 12.

[0039] The mould 28 is formed of a fixed block 30 which has aprotuberance 32 which has a shape complementary to that of the frontface 18 of the insert 12, which makes it possible on the one hand toposition the insert 12 in the mould 28 and on the other hand to preventthe insert 12 becoming deformed during moulding.

[0040] The mould 28 is also formed of a movable block 34 having animpression which defines a volume 36, with the rear face 22 of theinsert 12, when the mould 28 is closed.

[0041] The volume 36 is next filled with a thermoplastic substance inorder to form the body 16 of the reflector 10. The injected substance isa mixture of a thermoplastic material and a gas in liquid form. When thesubstance is inside the volume 36, the gas expands, to form a foam. Sucha substance and its use are for example described in the document EP-A-1040 158.

[0042] The formation of such a foam makes it possible to reduce theamount of material used.

[0043] When the foam forming the body 16 has cooled, that is to say ithas rigidified, the assembly is then removed from the mould and formsthe reflector 10.

[0044] It will also be understood that simple mechanical inversions canconstitute variant embodiments of the invention. For example, thematerial injected into the mould does not have to be in the form of afoam.

[0045] Furthermore, the coating of the sheet 14 can be carried outbefore the cutting thereof, that is to say when it is still in a roll.Deposition of the reflective layer 20 can then be performedcontinuously, hence a considerable time saving compared with the priorart where each optical reflector was coated one after another with thereflective layer.

[0046] One very important advantage of the invention is that it makes itpossible to deposit reflective layers on materials whose surfacecondition is not excellent: even with initial surface conditions ofaverage quality, reflectors of entirely satisfactory optical quality areobtained after deposition of the reflective layer. The appearanceconstraints which it was possible to have with the standard layerdeposition methods can thus be avoided. Consequently, polymer materialswith a significant filler level can be used for the materialconstituting the body of the reflector. These fillers can be introducedeither for cost reasons, or as a filler for strengthening the polymermaterial. With the invention, the proportion of filler in the polymercan be at least 10% by weight, and possibly up to 60% to 70% by weightof the total weight of the body of the reflector, while obtaining asatisfactory level of optical surface quality after deposition of thereflective coating. For constituting the polymer of the reflector, thechoice can be made for example from amongst one or more of the followingpolymers: polycarbonate, polyamide or polyethylene, either thermoplasticor thermosetting, preferably containing filler as mentioned above. Thefillers can be organic or mineral, for example based on carbon orcalcium carbonates, and can be in the form of particles, fibres, etc.

What is claimed is:
 1. A method of manufacturing a hollow opticalreflector of the type which comprises a rear body overmoulded around theconvex rear external face of a front insert, the concave front internalface of which is covered with a reflective layer, the method comprising:a step of producing the insert by forming; a step of overmoulding thebody on the insert; and a step of depositing the reflective layer on theconcave front face of the insert; wherein the step of depositing thereflective layer is prior to the forming step.
 2. A method according toclaim 1, wherein the step of forming the insert is a step ofthermoforming a sheet.
 3. A method according to claim 2, wherein themoulding step consists of injecting into a mould a mixture which iscomposed of the material constituting the body and a gas in liquid formand which is capable of forming a foam in the mould.
 4. A methodaccording to claim 1, wherein, during the moulding step, the front faceof the insert rests on a protuberance of a block of the mould which hasa shape complementary to that of the front face.
 5. An optical reflectorobtained according to the method in accordance with claim 1, wherein thematerial constituting the body of said reflector is based on polymer(s)with a proportion of filler of at least 10% by weight, in particularbetween 10% and 70% by weight.
 6. A motor vehicle lighting and/orsignalling device having at least one optical reflector according toclaim
 5. 7. A motor vehicle equipped with at least one device accordingto claim 6.